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ADSL Annex A
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ITU-T Standard G.992.1 that defines how ADSL works over plain old telephone
service (POTS) lines.
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ADSL Annex B
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ITU-T Standard G.992.1 that defines how ADSL works over Integrated Services
Digital Network (ISDN) lines.
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bandwidth on demand
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ISDN cost-control feature defining the bandwidth threshold that must
be reached on all links before a Services Router initiates additional
ISDN data connections to provide more bandwidth.
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basic rate interface (BRI)
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ISDN interface intended for home and small enterprise applications.
BRI consists of two 64-Kbps B-channels and one 16-Kbps D-channel.
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callback
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Alternative feature to dial-in that enables a J-series Services Router to
call back the caller from the remote end of a backup ISDN connection. Instead
of accepting a call from the remote end of the connection, the router rejects
the call, waits a configured period of time, and calls a number configured
on the router's dialer interface. See also dial-in.
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caller ID
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Telephone number of the caller on the remote end of a backup ISDN connection,
used to dial in and also to identify the caller. Multiple caller IDs can be
configured on an ISDN dialer interface. During dial-in, the router matches
the incoming call's caller ID against the caller IDs configured on its dialer
interfaces. Each dialer interface accepts calls from only callers whose caller
IDs are configured on it.
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channel service unit (CSU)
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Unit that connects a digital telephone line to a multiplexer or other
signal service.
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data service unit (DSU)
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Unit that connects a data terminal equipment (DTE) device—in this
case, a Services Router—to a digital telephone line.
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data terminal equipment–to–data communication
equipment (DTE–DCE) interface
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RS-232 interface that a Services Router (the DTE) uses to exchange
information with a serial device such as a modem (the DCE).
A DTE cable uses a male 9-pin or 25-pin connector, and a DCE cable uses
a female 9-pin or 25-pin connector.
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demand circuit
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Interface configured for dial-on-demand routing backup. In OSPF, the
demand circuit reduces the amount of OSPF traffic by removing all OSPF protocols
when the routing domain is in a steady state.
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dial backup
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Feature that reestablishes network connectivity through one or more
backup ISDN dialer interfaces after a primary interface fails. When the primary
interface is reestablished, the ISDN interface is disconnected.
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dial-in
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Feature that enables J-series Services Routers to receive calls from the
remote end of a backup ISDN connection. The remote end of the ISDN call might
be a service provider, a corporate central location, or a customer premises
equipment (CPE) branch office. All incoming calls can be verified against
caller IDs configured on the router's dialer interface. See also callback.
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dialer filter
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Stateless firewall filter that enables dial-on-demand routing backup
when applied to a physical ISDN interface and its dialer interface configured
as a passive static route. The passive static route has a lower priority than
dynamic routes. If all dynamic routes to an address are lost from the routing
table and the router receives a packet for that address, the dialer interface
initiates an ISDN backup connection and sends the packet over it. See also dial-on-demand
routing backup; floating static route.
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dial-on-demand-routing (DDR) backup
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Feature that provides a J-series Services Router with full-time connectivity
across an ISDN line. When routes on a primary serial T1, E1, T3, E3, Fast
Ethernet, or PPPoE interface are lost, an ISDN dialer interface establishes
a backup connection. To save connection time costs, the Services Router drops
the ISDN connection after a configured period of inactivity. Services Router with
ISDN interfaces support two types of dial-on-demand routing backup: on-demand
routing with a dialer filter and dialer watch. See also dialer filter;
dialer watch.
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floating static route
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Route with an administrative distance greater than the administrative
distance of the dynamically learned versions of the same route. The static
route is used only when the dynamic routes are no longer available. When a
floating static route is configured on an interface with a dialer filter,
the interface can be used for backup.
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dialer watch
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Dial-on-demand routing (DDR) backup feature that provides reliable connectivity
without relying on a dialer filter to activate the ISDN interface. The ISDN
dialer interface monitors the existence of each route on a watch list. If
all routes on the watch list are lost from the routing table, dialer watch
initiates the ISDN interface for failover connectivity. See also dial-on-demand
routing backup.
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“dying gasp” notification
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Ability of a Services Router with a digital subscriber line (DSL)
connection that has lost power to send a message informing the attached DSL
access multiplexer (DSLAM) that it is about to go offline.
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plain old telephone service (POTS)
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Standard telephone service that allows limited speed and bandwidth of
52 Kbps, which is also know as public switched telephone network (PSTN).
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ISDN S/T interface
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Interface between an ISDN network and a network termination device consisting
of two twisted pairs, one each for transmitting and receiving. The S/T interface
usually resides in the customer premises and operates at 192 Kbps, of
which ISDN traffic accounts for 144 Kbps.
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ISDN U interface
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Single twisted–pair interface line connecting the customer premises
unit in an ISDN network to the central office. A U interface runs at 144 Kbps
(128 Kbps for two B channels and 16 Kbps for the D channel).
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